DennisG

Hey there,
Thanks to all for all of the good info. and advice I've found here. A great resource for sure!

I've got a 2000 XJ, bone stock with 224K on the clock. I've got an issue with a very loud whistle which seems to come from right on or around the firewall. It's not constant, but consistent enough that it's almost predictable. It happens at idle, or low RPM, and goes away at higher RPM. I've been told by the family mechanics that it's a vacuum leak, which makes sense, but when I brought it to the shop, she refused to sing, so we weren't able to track it with carb clean or anything. I've got a check engine light, but the only code available was for an O2 sensor. I checked around the power booster, but that all seems well. The IAC was suggested as a possibility, but I haven't popped that off yet to check.

I've searched this forum, and found a bunch of possibilities, but I thought I'd take a stab, and see if anyone has experienced the same, or very similar symptoms, and what the cure might have been.

Any and all help and advice is certainly appreciated!

Thanks in advance, Dennis

Turbo X_J

Intake manifold.

stevecherokee

Bad alternator, or at least that was the solution to a similar -sounding symptom I had last year.

tjwalker

Get yourself a "mechanics stethoscope". Kind of like what the doctors use, but has an attenuator to filter out unwanted noises. Widely available and inexpensive. Belongs in everybody's toolbox.

Invaluable in tracking noises. Standard disclaimer; be careful poking around the engine bay.

tzaracki14

without a doubt an intake manifold gasket . I have a 2000 xj with 205000 on it and I had the exact same symptoms.. it would seldom do it when I wanted to do it.. but would always whistle on cold days only at low rpms and eventually got to the point where it would do it randomly but still at low rpms and would go away when the motor was revved.. I replaced my intake/exhaust gasket with a felpro one from orielys and problem was fixed.. spray some brake parts cleaner or carb cleaner around the intake gasket.. if your rpms change or the noise goes away for a while then you know that's the problem

Nottingham15

My '00 XJ had a similar whistle recently.
I had the serpentine belt off for another job and when I put it back on I made it tighter than it had been.
The whistle didn't sound remotely like a slipping belt but tightening the belt got rid of it. Maybe some kind of harmonic noise rather than air whistling through a hole??
Worth a try anyway - only costs a couple of minutes of your time and none of your cash to try it.

Grip

Check all vac lines before you start getting crazy with diagnosing or replacing crap.

Look at the crappy plastic tube that connects the PCV to the manifold.

Wiggle vac lines while it is idling to see if it will whistle.

ehall

does it happen when engine is warm or all the time

does it happen when moving or all the time

extrashaky

Yay! A voice of reason. I'm not sure where some of these other are coming from when OP clearly said the noise is coming from the rear of the engine bay and NOT from the belt or the alternator.

There are several ways to track down a vacuum leak, involving carb cleaner, water and even smoke. Find the leak first, THEN fix it.

I would put my money on the manifold gasket, but it would be really irritating to go to the trouble of replacing that only to have the problem come right back, especially when a little diagnostic effort would make it clear what needs to be fixed. Also, it probably doesn't actually need to be whistling for it to be leaking (and therefore detected).

TheGreatGazoo

Intake Manifold. just tighten down the bolts and you should be good. it happened to me about 3 years ago and 2 of my friends last summer. the last 3 bolts closest to the firewall.

DennisG

Thanks to all for the great advice!

Yes, I did forget to mention that it tends to idle rough, and the MPG has gone down, thus eliminating the alternator or other electrical possibility.

I'm intrigued by TheGreatGazoo's advice as I poked my head under the hood yesterday while she was squealing, and the noise definitely sounded like it was coming from a rear/central area. Not to mention, it's free and easy!

Now, is there a torque number that I need to adhere to, or just snug it up? I'm going to check it out tonight.

Thanks again!

ehall

rough idle indicates vaccum leak

best way to isolate whistling noise (if it happens when parked) is a 3-foot section of 1/2" rubber hose, stick one end in your ear and move the other around. The hose really picks up the high-pitched noises.

TheGreatGazoo

About 25 ft lbs. a little more than snug. there just in a bad spot to get to

aj2494

Just what Gazoo said. Be very gentle on them, especially on ones that are studs. If a stud gets broken off, it's not good. I did this recently and found that I needed a lot of extensions and I think I had to use a u-joint, so keep in mind that those affect the torque that is actually applied to the bolt/nut. For me, it didn't solve the issue so I'll be replacing the gasket soon. I'm confident that's the issue in my case.